The correct option is A.
Explanation
Geomorphic processes are classified into endogenic and exogenic forces based on their source of energy. Exogenic processes, also known as denudational processes, include weathering, mass wasting, erosion, and deposition. These processes act on the earth's surface to wear down relief features.
- The Sun: This is the primary source of energy for exogenic processes. Solar energy drives the Earth's atmospheric circulation and the hydrologic cycle. It determines temperature variations and precipitation patterns, which are the fundamental drivers of weathering and erosion by agents such as running water, glaciers, and wind.
- Tidal Friction: This is a minor force resulting from the gravitational interaction between the Earth, Moon, and Sun. While it affects oceanic tides and slightly slows Earth's rotation, it is not the ultimate driver of general denudational processes.
- Geothermal Gradients: This refers to the increase in temperature with depth within the Earth's interior. It is an internal energy source that drives endogenic processes like volcanism and tectonism, rather than exogenic ones.
- Radioactivity within the Earth: The decay of radioactive isotopes (like Uranium, Thorium, and Potassium) generates heat within the Earth's core and mantle. This heat is the primary energy source for endogenic forces, leading to plate movements and mountain building.
Key Takeaway: Exogenic processes derive their energy from the Sun and the gradients created by tectonic factors, whereas endogenic processes are driven by the internal heat of the Earth.